We plan to continue our examination of naturally aged cholesterol batches for their inherent mutagenicity towards test strains of Salmonella typhimurium. Naturally aged cholesterol is mutagenic towards several such strains, and we seek to determine which autoxidation products account for this biological activity. We shall continue to fractionate aged cholesterol preparations and assay such fractions for mutagenicity until active sub-fractions are found. Individual mutagenic sterols will be sought, their chemical identities established, and a thorough evaluation of their mutagenicities towards the bacterial strains made. Mutagenicity towards other test systems may also be conducted. Mutagenic sterols will be isolated by means of high performance liquid column chromatography, their identities established by chromatographic, spectral, and chemical evidence.